Tidal energy is renewable energy which is clean, environment-friendly and eco-friendly. And tides rise and fall each day, again and again, and the energy from tides is inexhaustible or can be used without limit.
Tidal energy is the potential energy of water formed by rising and falling of seawater, which is a relatively stable resource, and suffers scarcely from natural factors such as climates or hydrology. It can generate a steady amount of electricity, without dry years or wet years or being affected by wet or dry seasons, without the need of flooding vast farms to build reservoirs, thus without thorny problems such as population migration, flooding farms.
Currently, the common tidal power generation with successful application is to use hydrogenerators to convert the potential and kinetic energy of seawater into electrical power. However, owing to that a tidal power plants need to be built at a bay with deep waters and long dams, there are plenty of difficulties in construction, foundation treatment, silting prevention and the like, and civil works and electromechanical equipments cost highly. Meanwhile, to continuously generate power during all day, two reservoirs are needed for the tidal power plant, which doubles the works and cost thereof and affects its development and the utilization of tidal energy. Furthermore, not all the sea surfaces are appropriate for building dams to generate electricity, thereby constricting greatly the availability of tidal energy.
There is another way to utilize tidal energy: at rising and falling tide, a buoy performs a vertical movement respectively by a height equal to the difference of tide with its buoyancy when it is hermetic and empty, and with its gravity when it is full with water. The vertical movements of the buoy are transferred and converted so as to generate electricity.
With a review of various disclosures and designs with this principle, there are three types:
(1) the buoy drives directly a piston of an air cylinder to press air into a pressure tank, thereby converting tidal energy into compressed air and store it for power generation. However, due to the limitation of the prior fabrication technology and cost to an air cylinder with a long stroke and a large diameter, the design has not yet been put into industrial applications. (The difference of a tide ranges from 2 m to 15 m, usually 4-5 m, while an air cylinder with a stroke longer than 2 m and a diameter larger than 0.4 m is quite hard to make and cost much, and do not adapt to industrial applications).
(2) the buoy drives directly a piston of an hydraulic cylinder to lift sea water up to a reservoir at high location, thereby converting tidal energy into the potential energy of the water with high level for power generation. However, due to the limitation of the prior fabrication technology and cost to a hydraulic cylinder with a long stroke and a large diameter and due to the requirement of building a reservoir at high position, the design has not yet been put into industrial applications, either.
(3) the buoy drives mechanisms like gears, racks to move, thereby converting the tidal energy into torque force to drive gear box for power generation. However, due to the limitation of the prior fabrication technology and cost to a mechanism with a long stroke and due to that it doesn't involve the energy storage mechanism, the design has not yet been put into industrial applications.